In a fuel cell that generates electric power by using hydrocarbon fuel as it is, and in a fuel cell that generates the electric power by using reformed gas of the hydrocarbon fuel, a variety of fuel gases are used. Specifically, town gas, natural gas, gasoline, light oil and the like are used as the fuel gases. Among them, in such reformed fuel obtained by reforming the fuel such as the gasoline and the light oil once, and in the fuel such as the town gas, while large amounts of methane (CH4) and hydrogen (H2) are basically contained, small amounts of hydrocarbons with a carbon number of 2 or more, that is, ethane (C2H6), propane (C3H8), butane (C4H10), and the like are also contained.
For example, like a solid oxide fuel cell (SOFC), a fuel cell that operates at a somewhat high temperature is capable of generating the electric power even by using CH4. However, in the case of using hydrocarbon fuel with the carbon number of 2 or more in the solid oxide fuel cell, it has happened that carbon (C) is deposited on a surface of an electrode catalyst, whereby electrode activity is decreased. Specifically, when the number of moles of steam contained in the fuel gas supplied to a fuel electrode is not significantly large with respect to the number of moles of the carbon, it becomes impossible to completely oxidize the fuel. More specifically, in the case of using C3H8 as the fuel, when a ratio (S/C) of the steam and the carbon is not equal to 2 or more, it becomes impossible to completely oxidize C3H8. Therefore, it has happed that the carbon is deposited on the surface of the electrode catalyst, whereby the electrode catalyst is decreased.
In this connection, as a technology for preventing such the carbon deposition, a technology disclosed in Japanese Patent Unexamined Publication No. 2003-86225 is proposed. In this conventional technology, a steam supply device is disposed, the steam is supplied to the fuel electrode, a steam reforming reaction is caused, and the hydrocarbon is decomposed to carbon monoxide (CO) and the hydrogen (H2).